Accelerating Universe and Event Horizon

TL;DR

This paper investigates the long-term behavior of an accelerating universe with a constant equation of state parameter, showing it will accelerate indefinitely and possess an event horizon, challenging string theory compatibility.

Contribution

It demonstrates that a universe with a constant  = p/ remains eternally accelerating and has an event horizon, regardless of its energy composition.

Findings

Universe accelerates indefinitely with constant .

Such universe always exhibits an event horizon.

Implications for string theory compatibility.

Abstract

It has been argued in the literature that if a universe is expanding with an accelerating rate indefinitely, it presents a challenge to string theories due to the existence of event horizons. We study the fate of a currently accelerating universe. We show that the universe will continue to accelerate indefinitely if the parameter $\omega = p/\rho$ of the equation of state is a constant, no matter how many different types of energy (matter, radiation, quintessence, cosmological constant and etc) are contained in the universe. This type of universe will always exhibit an event horizon indicating that such a universe may not be derived from string theories. We also comment on some related issues.